The mass-storage market is currently dominated by magnetic hard drives, which are typically used up to the terabyte range. In the gigabyte range, solid-state Flash memory is most commonly used. Hard drives contain movable parts and are slower, less robust, and more power-hungry than solid-state memory.
Ideally, robust low-power terabyte storage should be obtained through a universal memory which is immune to the above limitations. However, a need for radiation hardness and non-volatility (retain memory state when power is off) make electrical charge storage like Flash unfeasible at the smallest scales, when a bit consists of only a hundred (or fewer) electrons, such as below a 35 nm technology node.
Such few stored electrons lead to significant statistical bit-to-bit variation, as well as poor charge retention, since long-term storage imposes drastic leakage current limits, of the order of one or two electrons per month. Another drawback of Flash is its high write/erase voltage (˜15 V), which is needed for tunneling in/out of the floating gate. Such voltages are incompatible with the low 1-2 V used in logic operation, and large-area charge pumps are often used for the step-up, consuming valuable on-chip real estate.
Table 1. Material properties used in simulation are described and shown in the specification.